Fluorescent backlit street signs have become the street sign of choice at critical intersections around the world. They make it very easy to identify street names at night, which reduces the level of distraction experienced by drivers unfamiliar with the location. This makes for safer intersections. The downside of these signs with fluorescent lights is they must be replaced approximately every eight months. The cost of the fluorescent tubes themselves is not too great, but the cost of the crew and equipment to perform the maintenance adds up. It is also a nuisance to properly dispose of the spent fluorescent bulbs.
It has been recognized that Light Emitting Diodes (LEDs) have the obvious advantage of having a much longer mean life between failure than do fluorescent bulbs. In many applications they also use significantly less power and are easier to dispose of. Others have already designed LED based products to replace fluorescent bulbs in backlit street signs. The current invention is proposed as an improvement that is achieved by different means. It provides better, more even lighting, is easier to install, and less costly to manufacture.
U.S. Pat. No. 6,761,471 issued on Jul. 13, 2004 discloses an LED assembly comprising an adjustable scissor mechanism employing principles of pressure and friction to secure the assembly. Also disclosed is the use of lenses as a means achieve an even distribution of light, as well as an alternative framework to achieve the same without the use of lenses.
U.S. Pat. No. 7,303,309 issued on Dec. 4, 2007 discloses a backlit sign comprising a housing with translucent, angled sidewalls and LED modules with lenses mounted to the top housing wall providing means to focus light on the sidewalls. Also disclosed is the use of a mirror on the bottom wall of the housing to further enhance the uniformity of lighting on the sidewalls.
U.S. Pat. No. 7,488,086 issued on Feb. 10, 2009, discloses an assembly comprising a linear LED array terminated at either end with electrical connectors compatible with fluorescent tube receptacle. A mirror reflector can be mounted on an opposing wall to distribute the light a little more evenly. Further disclosed is that the cross section of the assembly can be different shapes, but still resulting in an essentially one dimensional array intended to duplicate the light emitting characteristics of a fluorescent tube.
U.S. patent application Ser. No. 11/411,674 filed on Apr. 26, 2006, discloses a contoured mounting device for LEDs of one or more colors so as to best match the illumination requirements of a sign.
U.S. Pat. No. 6,853,151 issued on Feb. 8, 2005 and U.S. Pat. No. 6,762,562 issued on Jul. 13, 2004 disclose a basically tubular LED assembly that mechanically and electrically installs in the same manner as the fluorescent tube it is designed to replace. It comprises the necessary electronics to convert the electrical power supplied by the fluorescent ballast to meet the needs of the LED assembly.
U.S. Pat. No. 6,739,734 issued on May 25, 2004 discloses an assembly comprised of a basically flat sheet of relatively stiff material with LED modules affixed to it. Also disclosed is that the LED assembly and power supply are mounted independently to the housing by undisclosed means.
U.S. Pat. No. 6,936,968 issued on Aug. 30, 2005 discloses an LED assembly within a clear cylindrical enclosure. There is a means on either end of the assembly to install into a fluorescent tube receptacle and make electrical contact. There is no claim of using power from the fluorescent ballast.
U.S. Pat. No. 6,924,973 issued on Aug. 2, 2005 discloses an LED module suitable for backlighting signs, the module comprising means to provide protection from hostel environments and to convert AC line current to power the LED.
None of the prior art discloses an LED assembly comprising LED modules; said modules comprised of a PCB assembly; said PCB assembly comprised of a long slender PCB, a linear array of LEDs along its length, current conditioning electronics, a means of attachment to the assembly, and a coating to protect against environmental conditions such as humidity; said LED modules themselves being arranged in a linear array on a simple, lightweight structural frame, resulting in a uniform two dimensional array of LEDS ideally suited to providing either direct uniform area lighting or direct uniform backlighting of translucent signs. Furthermore, none of the prior art discloses, in the instance of retrofitting fluorescent tubes with an LED assembly, the use of the fluorescent receptacles solely as a mechanical means of attachment, completely abandoning their electrical function. Still furthermore, none of the prior art discloses the use of commercially available, environmentally sealed, high efficiency, switching power supplies mounted to either the lightweight frame of the LED assembly or the housing of the fixture.
In accordance with the present invention there is provided a low-cost, environmentally hardened, reliable LED assembly designed and configured provide uniform lighting and trouble-free use in applications requiring minimal maintenance and maximum lifetime. Furthermore, the simplicity of design makes the assembly extremely easy to install whether being put directly into an OEM fixture, or being used to retrofit an existing fluorescent fixture.